Sea lice parasites cause direct welfare harm to farmed salmon through feeding on skin and blood. Understanding their biology helps develop more welfare-conscious management strategies.
Sea lice welfare impacts on farmed salmon are both direct and indirect. Directly, feeding lice cause tissue damage through skin lesions that range from minor irritation to severe open wounds exposing underlying muscle. The feeding activity itself is a nociceptive stimulus. Heavily infested salmon show behavioral changes including increased surfacing, flashing, and reduced feeding — behavioral indicators consistent with discomfort. Indirectly, lice management through chemical treatments, physical handling, and thermal treatment causes welfare costs from the treatment procedures. The ideal welfare outcome — low lice levels without frequent treatment — requires either effective biological controls, lower stocking densities, or genetic resistance, all of which are active areas of development.